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991.
The incipient separation induced by the shock wave/turbulent boundary layer interaction at the sharp fin is the subject of the present study. Existing theories for the prediction of incipient separation, such as those put forward by McCabe (1966) and Dou and Deng (1992), can thus far only predic the direction of surface streamline and tend to overpredict the incipient separation condition based on the Stanbrook’s criterion. In this paper, the incipient separation is first predicted with Dou and Deng (1992)’s theory and then compared with Lu and Settles’ (1990) experimental data. The physical mechanism of the incipient separation as induced by the shock wave/turbulent boundary layer interactions at sharp fin is explained via surface flow pattern analysis. Furthermore, the reason for the observed discrepancy between the predicted and experimental incipient separation conditions is clarified. It is found that when the wall-limiting streamlines behind the shock wave becomes aligned with one ray from the virtual origin as the strength of the shock wave increases, the incipient separation line is formed at which the wall-limiting streamline becomes perpendicular to the local pressure gradient. The formation of this incipient separation line is the beginning of the separation process. The effects of Reynolds number and Mach number on incipient separation are also discussed. Finally, a correlation for the correction of the incipient separation angle as predicted by the theory is also given.
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992.
Hua-Shu Dou Boo Cheong Khoo Nhan Phan-Thien Khoon Seng Yeo Rong Zheng 《Rheologica Acta》2007,46(4):427-447
The simulation of fibre orientation in dilute suspension with front moving is carried out using the projection and level-set
methods. The motion of fibres is described using the Jeffery equation, and the contribution of fibres to the flow is accounted
for by the configuration-field method. The dilute suspension of short fibres in Newtonian fluids is considered. The governing
Navier–Stokes equation for the fluid flow is solved using the projection method with finite difference scheme, while the fibre-related
equations are directly solved with the Runge–Kutta method. In the present study for fibres in dilute suspension flow for injection
molding, the effects of various flow and material parameters on the fibre orientation, the velocity distributions and the
shapes of the leading flow front are found and discussed. Our findings indicate that the presence of fibre motion has little
influence on the front shape in the ranges of fibre parameters studied at the fixed Reynolds number. Influence of changing
fibre parameters only causes variation of front shape in the region near the wall, and the front shape in the central core
area does not vary much with the fibre parameters. On the other hand, the fibre motion has strong influence on the distributions
of the streamwise and transverse velocities in the fountain flow. Fibre motion produces strong normal stress near the wall
which leads to the reduction of transversal velocity as compared to the Newtonian flow without fibres, which in turn, leads
to the increased streamwise velocity near the wall. Thus, the fibre addition to the flow weakens the strength of the fountain
flow. The Reynolds number has also displayed significant influence on the distribution of the streamwise velocity behind the
flow front for a given fibre concentration. It is also found that the fibre orientation is not always along the direction
of the velocity vector in the process of mold filling. In the region of the fountain flow, the fibre near the centreline is
more oriented across the streamwise direction compared to that in the region far behind the flow front. This leads to the
fact that the fibre near the centreline in the region of fountain flow is more extended along the transverse direction. As
the fibre orientation in the suspension flow and the shape of the flow front have great bearing on the quality of the product
made from injection molding, this study has much implications for engineering applications. These results can also be useful
in other fields dealing with fibre suspensions. 相似文献
993.
994.
膦类离子液体,因其好的热稳定性以及在弱碱性介质中的惰性等优异特点,正在受到越来越多的关注.以廉价的三丁基膦和各种卤代烃为原料,制备了一系列季膦离子液体,然后以其与水组成的复合体系为反应介质,在催化剂1,4-二氮杂二环[2.2.2]辛烷(DABCO)作用下,进行了各种醛与丙烯腈、丙烯酸甲酯及丙烯酰胺的Morita-Baylis-Hillman反应研究.实验结果表明,在室温条件下,溴化乙基三丁基膦与水组成的复合溶剂体系,有效地促进了各种芳香醛及脂肪醛的Morita-Baylis-Hillman反应,不仅反应速度快,而且目标产物产率高. 相似文献
995.
Chuandong Dou Zicheng Ding Zijian Zhang Zhiyuan Xie Jun Liu Lixiang Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(12):3719-3723
The key parameters of conjugated polymers are lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels. Few approaches can simultaneously lower LUMO and HOMO energy levels of conjugated polymers to a large extent (>0.5 eV). Disclosed herein is a novel strategy to decrease both LUMO and HOMO energy levels of conjugated polymers by about 0.6 eV through replacement of a C C unit by a B←N unit. The replacement makes the resulting polymer transform from an electron donor into an electron acceptor, and is proven by fluorescence quenching experiments and the photovoltaic response. This work not only provides an effective approach to tune the LUMO/HOMO energy levels of conjugated polymers, but also uses organic boron chemistry as a new toolbox to develop conjugated polymers with high electron affinity for polymer optoelectronic devices. 相似文献
996.
Analysis of small interfering RNA by capillary electrophoresis in hydroxyethylcellulose solutions 下载免费PDF全文
Chenchen Liu Yoshinori Yamaguchi Xifang Zhu Zhenqing Li Yi Ni Xiaoming Dou 《Electrophoresis》2015,36(14):1651-1657
The analysis of small interfering RNA (siRNA) is important for gene function studies and drug developments. We employed CE to study the separation of siRNA ladder marker, which were ten double‐stranded RNA (dsRNA) fragments ranged from 20 to 1000 bp, in solutions of hydroxyethylcellulose (HEC) polymer with different concentrations and molecular weights (Mws). Migration mechanism of dsRNA during CE was studied by the mobility and resolution length (RL) plots. We found that the RL depended on not only the concentration of HEC, but also the Mw of HEC. For instance, RL of small dsRNA fragment was more influenced by concentration of high Mw HEC than large dsRNA fragment and RL of large dsRNA fragment was more influenced by concentration of low Mw HEC than small dsRNA fragment. In addition, we found electrophoretic evidence that the structure of dsRNA was more compact than dsDNA with the same length. In practice, we succeeded to separate the glyceraldehyde 3‐phosphate dehydrogenase siRNA in the mixture of the siRNA ladder marker within 4 min. 相似文献
997.
A new and simple series of side-chain liquid crystalline polymethacrylates containing biphenyl hemiphasmidic mesogens based on 4-[(3,4,5-trialkan)-1-carbonylbenzoate]biphenyl (denoted as PTmBMA, m = 6, 8, 10, 12, 14, 16, 18, m refers to the carbon number of alkoxy tails) groups was designed and successfully synthesised via free radical polymerisation. The phase structures and transitions of the polymers were investigated by the combination of techniques including differential scanning calorimetry, polarizing microscope, one-dimensional/two-dimensional wide-angle X-ray diffraction, and small-angle X-ray scattering. The experimental results revealed that the liquid crystalline phase structures and behaviours of the polymers were found to be strongly dependent on the alkyl tail length (m). When m = 6, the PTmBMA formed a stable smectic phase above Tg. When m = 8, 10, 12, 14, 16, 18, the sample presented a hexagonal columnar mesophase (Φh), suggesting that the alkyl length has played an important role in the phase behaviours of hemiphasmidic side-chain liquid crystalline polymers. 相似文献
998.
对GB/T 7494–1987测定地表水中阴离子表面活性剂含量的方法进行优化。对萃取次数、磷酸二氢钠溶液反洗以及pH调节等进行了试验研究,将萃取用的三氯甲烷总量降为25 mL,两次萃取定容后一次反洗。结果表明,萃取两次可以满足分析需求,反洗能够有效去除亚硝酸盐氮等离子干扰,中性地表水样品无需调节pH,非中性样品须调为中性后测定。方法优化后线性良好,线性相关系数大于0.999,检出限为0.012 mg/L。测定结果的相对标准偏差为0.8%~3.3%(n=6),加标回收率为92.0%~110.0%。优化后方法满足地表水分析要求,能有效降低三氯甲烷用量并简化分析步骤。 相似文献
999.
Two wide bandgap (WBG) conjugated polymers, P2T-DTTTAZ and P2T-DTTAZ, with donor-π-acceptor (D-π-A) structures was designed and synthesized, utilizing thieno[3,2-b]thiophene (TT) and/or thiophene (T) units as π-bridge in conjugated polymer backbone. And, the wider optical band gap (Eg) of approximately 1.98 eV for P2T-DTTTAZ and 2.09 eV for P2T-DTTAZ were observed. Obviously, replacing T unit with larger conjugated plane TT unit as π-bridges, P2T-DTTTAZ resulted in the red shifted absorption and the reduced band gap, compared with these of P2T-DTTAZ. The polymer solar cells (PSCs) with an inverted device structure based on P2T-DTTTAZ or P2T-DTTAZ as donor and [6,6] phenyl-C61 butyric acid methyl ester (PC61BM) as acceptor were assembled and the photovoltaic properties were also investigated. The power conversion efficiencies (PCEs) of 1.57% for P2T-DTTTAZ and 1.25% for P2T-DTTAZ were obtained. 相似文献
1000.
Microchimica Acta - The article describes a sensitive and rapid method for the colorimetric determination of Salmonella pullorum and Salmonella gallinarum (S. pullorum and S. gallinarum). Silica... 相似文献